1. Field of the Invention
The present invention relates to a method of controlling an industrial robot such as a welding robot, and more particularly to a method of controlling the robot to perform a weaving action while tracking an operation line using a non-contact sensor such as a laser sensor.
2. Description of the Related Art
Known in the related art of robot control technology is a tracking method using a non-contact sensor. In this method, a position of an operation line such as a welding line is successively detected by the non-contact sensor such as a laser sensor, mounted on the robot for sensing an advanced region of a tool in a moving direction of the tool during a play-back operation of an operation program. In addition, a taught path is corrected according to the result of the detection received from the non-contact sensor. The non-contact sensor is hereinafter represented by the laser sensor.
The above tracking control method by correcting the taught path using a laser sensor enables the robot to trace the operation line detected by the laser sensor even if an object of operation (workpiece) is not precisely positioned, to provide a very useful technology to a welding robot, etc.
On the other hand, in a welding robot, etc., a control method for performing a weaving action of periodically displacing the tool from a predetermined reference path is widely adopted. The conventional weaving action is performed by employing the taught path as a reference path. However, in a case where an actual welding line is possibly deviated from the taught path, it is desirable to perform the weaving action by employing a welding line considerably deviated from the taught path as the reference path.
In tracking the welding line using a laser sensor, so as to obtain a tracking target point (a crossing point of the scanning locus and the welding line) in a robot coordinate system set to the robot (e.g. a base coordinate system set to a base of the robot) on the basis of the detection data from the laser sensor, it is necessary to determine a robot position at each time of the scanning periodically performed by the laser sensor.
In tracking without the weaving action, as the robot position at each time of scanning by the laser sensor can be definitely calculated from the position data of the taught path and the detection data from the sensor, it is possible to control the robot by successively determining a tracking target point.
However, when the robot is controlled to perform the weaving action, the robot position at each scanning time would be largely changed due to the displacement amount (weaving amount) added for the weaving action. Therefore, unless the weaving amount at each scanning time is calculable, already known or constant, it is impossible to control the robot to perform the weaving action while tracking the welding line as a reference line of the weaving. In the conventional art, since an accurate displacement amount for the weaving at each scanning of the laser sensor could not be obtained, it was difficult to realize the tracking with the weaving action.